This invention relates generally to audio codecs for processor-based systems.
An audio codec receives digital audio information, converts it to an analog format and mixes that audio information with other data for play by a processor-based system. Generally, the codec is controlled by an audio controller, also known as an audio accelerator, coupled to a bus. The audio accelerator is in turn controlled by the processor.
Many processor-based systems are now being used for relatively elaborate audio functions. For example, processor-based systems may be used to receive digital radio, television and stereo system signals and to play those signals in a unified system. Digital television signals may be received through a cable or satellite connection. In addition, processor-based systems may be utilized to record digital audio information received from a variety of sources.
Conventional codecs, however, handle one audio program at any one time. For example, the Audio Codec '97 (AC'97) Specification, Revision 2.1, dated May 22, 1998, available from Intel Corporation, describes an audio codec that receives a digital stereo channel pair and converts that pair into an analog stereo channel pair. The term “pair” refers to the two channels conventionally called the left and the right channels in stereo systems. The converted analog stereo channel pair may be mixed with other information in a mixer within the codec. The mixer is also coupled to an analog to digital converter that provides an output from the mixer to the digital link.
The AC'97 codec is amenable to handling only one audio program at a time. It is not amenable, for example, to simultaneously recording and playing a television program.
Thus, there is a need for a codec that supports the increasing demands being placed on processor-based systems for handling more than one audio program at a time.